Carburetor ambient mixture control

ABSTRACT

The carburetor has an air bypass passage for supplying additional air around the venturi to the air/fuel mixture in response to ambient operating conditions, the air bypass passage being controlled by valve means sensitive to changes in ambient conditions and including an additional air bleed for supplying air to the bypass passage when the carburetor choke valve is closed so as to lean out the overrich mixture that would normally be provided with changes in ambient operating conditions if such an air bleed were not provided.

United States Patent [191 Lunsford [451 Sept. 17, 1974 CARBURETOR AMBIENT MIXTURE CONTROL [75] Inventor: Max W. Lunsford, Southfield, Mich.

[73] Assignee: Ford Motor Company, Dearborn,

Mich.

[22] Filed: Nov. 3, 1972 [21] Appl. No.: 303,572

[52] US. Cl. 261/39 A, 261/63 [51] Int. Cl. F02m 7/20 [58] Field of Search 261/39 A, 63, 41 D, DIG. 56

[56] References Cited UNITED STATES PATENTS 2,230,159 l/1941 Kratzer 261/39 A X 3,011,770 12/1961 Stoltman 261/39 A 3,186,692 6/1965 Moseley 261/39 B Primary Examiner-Andre w R. Juhasz Assistant Examiner-Z. R. Blinsky Attorney, Agent, or Firm-l(. L. Zerschling; R. E. McCollum [5 7 ABSTRACT The carburetor has an air bypass passage for supplying additional air around the venturi to the air/fuel mixture in response to ambient operating conditions, the air bypass passage being controlled by valve means sensitive to changes in ambient conditions and inc1uding an additional air bleed for supplying air to the bypass passage when the carburetor choke valve is closed so as to lean out the overrich mixture that would normally be provided with changes in ambient operating conditions if such an air bleed were not provided.

2 Claims, 2 Drawing Figures CARBURETOR AMBIENT MIXTURE CONTROL This invention relates, in general, to a carburetor for an internal combustion engine. More particularly, it relates'to one that compensates for the change in density of the air due to changes in altitude and temperature.

Most production type carburetors in use today have no means for correcting the carburetor airflow requirements to compensate for changes in air density as a re sult of changes in altitude or temperature. As a result, increases in altitude cause a richening of the mixture and consequently off-design operation. This is especially noticeable during cold starting operating when the conventional choke valve is closed to provide a rich starting mixture. More specifically, as altitude increases, the lower density of the air coupled with the lower volume of air as a result of closing of the choke valve will result in an overrich starting mixture.

Carburetor constructions are known in which air bypass passages are provided to vary the supply of air when ambient operating conditions change. For example, Stoltman US. Pat. No. 3,011,770, Altitude Compensated Carburetor, shows such an air bypass passage that is controlled by a bellows to provide additional air as required by the chaning ambient operating conditions. The air bypass passage has an inlet connected to the induction passage between the choke valve and the venturi and an outlet connected to portions both above and below the conventional throttle valve. The outlet connection as described permits correction for changing ambient operating conditions during engine idle speed operation as well as other periods. As the altitude increases, the lowering density of the air is offset by the increase of air through the bypass passage.

While the Stoltman device shows compensating means for correcting for changes in air density, it does not provide additional air for leaning out the starting mixture when the choke valve is closed during cold weather operation. That is, when the choke valve of the Stoltman device is closed, the additional air bypass passage also is effectively blocked off and, accordingly, the starting mixture will be richer than desired, in the manner stated above.

The invention eliminates the above objection by providing a construction in which an air supply is maintained and controlled during the choking operation as well as at other times so that the air/fuel mixture is compensated during all engine operations for changes in air density or temperature.

It is a primary object of the invention, therefore, to provide a carburetor construction that is sensitive to ambient operating conditions to compensate for changes in air density and temperature and thus provide essentially a constant calibrated fuel/air ratio for any given operating condition of the engine.

It is another object of the invention to provide a carburetor with an air bypass flowing air around the carburetor venturi, the passage being controlled by valve means that is responsive to ambient temperature and pressure changes to compensate for changes in air density, and an additional air passage being provided to maintain a controlled supply of air to the air passage when the choke valve is moved towards a closed position normally terminating flow to the air passage.

Other objects, features and advantages of the invention will become more apparent upon reference to the succeeding detailed description thereof, and to the 2 drawing illustrating the preferred embodiments thereof; wherein,

FIG. 1 is a schematic crosssectional view of a portion of a carburetor embodying the invention; and,

FIG. 2 is a modification of the design shown in FIG. 1.

FIG. 1 shows a portion 10 of a downdraft type carburetor. It includes the usual air induction passage 12 having one end 14 open to air at essentially atmospheric pressure. Its other end 16 is adapted to be connected to the intake manifold of an internal combustion engine, not shown, so as to subject the induction passage to the changes in engine vacuum level. The passage 12 includes the usual choke valve 18 unbalance mounted on a shaft 20 rotatably mounted in the walls of the air horn section of the carburetor. The choke valve is variably rotatable by the usual mechanism, not shown, from the closed position shown to a nearly vertical position permitting unrestricted flow of air through the induction passage.

Passage 12 also includes a conventional venturi 22 into which is inducted, in a known manner, the main supply of fuel through a tube 24 where it is mixed with the air from inlet 14 for flow past a throttle valve 26. The latter is mounted on a shaft 28 rotatably mounted in the walls of the carburetor body.

Further details of construction and operation of the carburetor per se are notgiven since they are known and are believed to be unnecessary for an understanding of the invention. Suffice it to say that during normal cold start operations, the choke valve 18 is in the essentially closed position shown restricting airflow through the carburetor. The strong vacuum signal from the engine pistons causes a supply of fuel to be drawn from the idle system, not shown, and mixed with the small amount of air available so that the starting mixture is very rich. As soon as the engine is started, the conventional dechoking mechanism will crack open the choke valve 18 by a slight amount sufficient to permit continued operation of the engine at a leaner air/fuel ratio.

In this instance, the carburetor body is provided with an air bypass passage 30 that has an air inlet 32 opening into induction passage 12 between the choke valve 18 and the inlet to venturi 22. The air in inlet 32, therefore, is essentially at atmospheric pressure level. One discharge 34 of the air passage is located below venturi 22 so as to be closer to an atmospheric pressure level than the reduced pressure obtained at the throat of venturi 22. The reason for bypassing the venturi, of course, is so that the additional airflow supplied through passage 30 will not cause any additional flow of fuel from the nozzle 24.

The passage 30 has an additional discharge outlet 36 located below the closed position of throttle valve 26 to provide additional air during closed throttle, engine idle speed operation.

Airflow through passage 30 is controlled in this instance by a valve means 38 that is movable in response to ambient operating changes. More specifically, the valve means has a lower needle like valve 40 adapted to cooperate with a valve seat 42 formed in the throttle flange portion 44. It further includes a conical valve 46 that is biased against a seat 48 by a spring 49 to block or open in a variable manner the flow of air to both passages 34 and 36. The conical valve portion 46 has a stem actuator 50 extending through an aperture 52 in the carburetor body for connection with one end of a lever 53. The latter is hinged at 54 and movable by an aneroid or bellows 56.

The bellows 56 defines a sealed interiorchamber under atmospheric or some similar reference pressure, a change in the ambient pressure and temperature conditions causing the bellows or aneroid to exert a force upon the connecting lever 53 to move the valve 38 upwardly or downwardly, as the case may be, to thereby vary the airflow through the bypass passage 30.

Completing the construction, the carburetor body is provided with a further air inlet hole 60 of a controlled size that, in a manner to be described, continues to supply air to the passage 30 even though the air inlet 32 is essentially closed when the choke valve 18 is closed.

In operation, when the ambient operating conditions are the same as the reference used for the interior of bellows 56, then the parts will be positioned as shown with the additional air passage 30 closed. The carburetor then will operate in a conventional manner with no additional air being added to the air/fuel mixture inducted into the intake manifold portion 16. As the ambient temperature increases, or if the altitude rises, the density of the air taken into the carburetor will also change. However, since the induction of fuel and air through the carburetor is on a volume basis rather than by weight, there will be a change in the air/fuel ratio with a resultant richening of the mixture. However, with the construction as shown, a rise in the temperature level or increase in altitude will cause the bellows 56 to raise the rod 53 and valve 38 against the bias of spring 49 to open the air passage 30 for bypass of air around the venturi 22. Accordingly, additional air will be added to the air/fuel mixture to compensate for the loss in density, resulting in a substantially constant air/fuel ratio for the particular engine speed and load.

During idle speed operation, throttle valve 26 will be essentially closed. Accordingly, compensation for changes in density at this time will be made by the addition of air through the discharge passage 36 instead of the passage 34.

During choking operation, the choke valve 18 is essentially closed in the position shown. Accordingly, at this time, the air inlet 32 would also be essentially closed and no additional air would flow through the passage 30. However, the inclusion of the aperture 60 of a controlled size permits a controlled quantity of air to be added to the air passage 30 for passage into either of the discharge portions 34 or 36. This results in a leaning of the choking mixture to the level provided at other ambient operating conditions.

FIG. 2 shows a modified form of valve 38 for control of the starting mixture when the choke valve 18 again is closed. In this instance, a conical needle-like valve 70 is added to the stem 50' of valve 38' and cooperates with an opening 52 to variably increase the airflow into bypass passage 30 with changes in ambient operating conditions. Accordingly, the choking mixture will be controlled in a variable manner as a function of the changes in ambient operating conditions.

While the invention has been described and shown in its preferred embodiments, it will be clear to those skilled in the arts to which it pertains that many changes and modifications may be made thereto without departing from the scope of the invention.

1 claim:

1. A carburetor having an induction passage connected to air at one end and to an engine intake manifold at the opposite end and having a venturi in be tween adapted to be connected to a source of fuel for the induction thereof into the passage in response to airflow therepast, a choke valve mounted anterior of the venturi and rotatable at times to control airflow therepast, an air passage for supplying air directly to the induction passage below the venturi, ambient pressure and temperature responsive means for controlling the overall air/fuel ratio in the intake manifold by controlling airflow through the air passage to compensate for changes in air density with changes in altitude and temperature, and separate means to maintain a controlled supply of air to the air passage when the choke valve is rotated to a choking position, the separate means comprising an air bleed opening of a controlled size, valve means movably mounted with respect to the air bleed opening to variably control the flow therethrough, and means connecting the valve means to the ambient pressure and temperature responsive means.

2. A carburetor having an induction passage connected to air at one end and to an engine intake manifold at the opposite end and having a venturi inbetween adapted to be connected to a source of fuel for the induction of fuel into the passage in response to airflow therepast, a choke valve mounted anterior of the venturi and rotatable at times to control airflow through the passage, an air passage for bypassing air around the venturi, the air passage being connected at its air'inlet end to the induction passage between the choke valve and the venturi and at its other end to the induction passage below the venturi, valve means movable in response to ambient pressure and temperature changes for controlling airflow through the air passage to compensate for changes in air density with changes in altitude and temperature, and additional air inlet means for supplying air to the air passage when the choke valve is rotated to a choking position essentially closing the air passage air inlet, the additional air inlet means comprising an air bleed connected to the air passage outside of the induction passage and in a parallel flow relationship with the air inlet to the air passage, and second valve means movably mounted with respect to the air bleed to variably control flow therethrough, and connected to the first mentioned valve means for movement therewith. 

1. A carburetor having an induction passage connected to air at one end and to an engine intake manifold at the opposite end and having a venturi in between adapted to be connected to a source of fuel for the induction thereof into the passage in response to airflow therepast, a choke valve mounted anterior of the venturi and rotatable at times to control airflow therepast, an air passage for supplying air directly to the induction passage below the venturi, ambient pressure and temperature responsive means for controlling the overall air/fuel ratio in the intake manifold by controlling airflow through the air passage to compensate for chAnges in air density with changes in altitude and temperature, and separate means to maintain a controlled supply of air to the air passage when the choke valve is rotated to a choking position, the separate means comprising an air bleed opening of a controlled size, valve means movably mounted with respect to the air bleed opening to variably control the flow therethrough, and means connecting the valve means to the ambient pressure and temperature responsive means.
 2. A carburetor having an induction passage connected to air at one end and to an engine intake manifold at the opposite end and having a venturi inbetween adapted to be connected to a source of fuel for the induction of fuel into the passage in response to airflow therepast, a choke valve mounted anterior of the venturi and rotatable at times to control airflow through the passage, an air passage for bypassing air around the venturi, the air passage being connected at its air inlet end to the induction passage between the choke valve and the venturi and at its other end to the induction passage below the venturi, valve means movable in response to ambient pressure and temperature changes for controlling airflow through the air passage to compensate for changes in air density with changes in altitude and temperature, and additional air inlet means for supplying air to the air passage when the choke valve is rotated to a choking position essentially closing the air passage air inlet, the additional air inlet means comprising an air bleed connected to the air passage outside of the induction passage and in a parallel flow relationship with the air inlet to the air passage, and second valve means movably mounted with respect to the air bleed to variably control flow therethrough, and connected to the first mentioned valve means for movement therewith. 